It is the purpose of this paper to design the most preferable method of erythropoietin bioassay in Korea. Bioassay utilizing polycythemic mice are currently in general use for the indirect determination of erythropoietin. Assay animals are usually prepared either by transfusion or by exposure to reduced oxygen tension in specially constructed chamber. We prepared the polycythemic mice by the specially constructed hypobaric chamber. We observed weights and hematocrits of the mice in the hypobaric chamber, then hematocrits and 72 hours 59Fe red cell upatke ratio of the polycythemic mice induced by hypoxia after removal from the hypobaric chamber. We designed the method of erythropoietin bioassay according to the results obtained by above experiments. Then we measured the 72 hours 59Fe red cell uptake ratio of the polycythemic mice with normal saline, normal plasma and anemic plasma according to the method we designed. The results are followed:1) The hematocrits of the mice in hypobaric chamber increased to 74% in 11 days. It is preferable to maintain the pressure of the chamber to 400mmHg for first 4 days then 300mmHg for last 10 days to reduce the death rate and time consuming in hypobaric chamber. 2) After removal from the hypobaric chamber, the 72 hours 59Fe red cell uptake ratio decreased rapidly and maintained the lowest level from the fourth day to tenth day. 3) We design the method of erythropoietin bioassay arcording to the resuits of above experiment and to the half life of erythropoietin. 4) The Korean product 59Fe is mixture of 55Fe and 59Fe. And the 59Fe red cell uptake ratio in normal mice was far less with Korean product 59Fe than with pure 59Fe of foreign product. So it is desirable to use pure 59Fe in this method of erythropoietin bioassay. 5) Considering the cost, the technique, the time consuming and the sensitivity it is the most preferable method of erythropoietin bioassay in Korea using hypobaric chamber to induce the polycythemia.